This invention relates in general to high strength, light weight structural components and, more specifically, to the manufacture of stabilized skin structures having a plurality of spheres bonded between spaced skin sheets.
High strength, light weight structures are required in many applications, particularly in aircraft and space vehicles. Many such structures have been designed, of widely varying effectiveness and cost.
Isogrid panels, for example, in which a metal plate is machined to produce a panel having a triangular pattern of upstanding ribs and a thin face sheet are very effective. Typical isogrid panels are described in U.S. Pat. No. 4,801,070. The rib pattern can be easily varied in accordance with local area strength requirements. However, these panels are very expensive due to the large amount of metal which must be machined away and the extreme accuracy and care required in the machining operation. Also, they have a skin surface on only one side of the structure.
Honeycomb core panels, large diameter tubular structures and other shapes in which a metal honeycomb sheet is bonded, such as by brazing, between two metal face sheets to form a stabilized skin structure have come into widespread use. Typical of such panels are those described in U.S. Pat. No. 4,716,067. These panels are fairly easy, and only moderately expensive, to manufacture in simple shapes, such as flat or slightly curved panels or large radius tubes. It is, however difficult to meet requirements for local area strengthening of the structure where, for example, connections for other structures must be inserted into the structure. Also, complex shapes are difficult to fabricate as are structures or panels having varying thickness.
Fairly lightweight panels have been made by incorporating lightweight particles, such as vermiculite, glass, plastic or metal microballoons into a plastic matrix and forming structures from the mixture. While these materials may be formed into a variety of complex structures, they tend to be heavy and it is difficult to vary structural strength and weight in different areas. Also, they are not suitable for applications where an all-metal structure is required.
Very small hollow metal microspheres having diameters from about 200 to 10,000 microns have been made as described in U.S. Pat. No. 4,582,534. These microspheres may be fused together or bonded in a glass or resin matrix to produce panels or other structures. While complex shapes can be produced from these materials, the microsphere manufacturing process seems complex and expensive and the strength of panels cannot be easily varied in local areas. Because of the small microsphere diameters, these panels tend to be heavy.
Thus, there is a continuing need for improved panels and other structures which combine light weight, high strength, ease of manufacture, low cost and the ability to easily vary the structural strength in local areas.